Liquid crystal display device having variable viewing angle

ABSTRACT

A liquid crystal display device having variable viewing angles includes a first liquid crystal cell having first and second substrates spaced apart from and facing each other, a pixel electrode formed on an inner surface of the first substrate, a common electrode formed on an inner surface of the second substrate, and a first liquid crystal layer interposed between the pixel electrode and the common electrode; a second liquid crystal cell on the first liquid crystal cell, the second liquid crystal cell having third and fourth substrates spaced apart from and facing each other, and two alignment layers, wherein the first and second alignment layers are arranged to have holographic patterns; and a switching part for selectively applying electric field to the second liquid crystal.

This application is a Divisional of Application Ser. No. 10/734,180filed Dec. 15, 2003 now U.S. Pat. No. 7,068,336, which is herebyincorporated by reference as if fully set forth herein. This applicationclaims the benefit of Korean Patent Application Nos. 2002-079852 filedin Korea on Dec. 13, 2002 and 2002-083200 filed in Korea on Dec. 24,2002, which are hereby incorporated by reference for all purposes as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) deviceand more particularly, to a liquid crystal display device havingvariable viewing angles.

2. Discussion of the Related Art

Cathode ray tubes (CRTs) have been widely used as a display devices fortelevisions and a computer monitors. However, the cathode ray tube has alarge size, heavy weight, and high driving voltage. Therefore, flatpanel displays, being thin, light weight, and low in power consumptionare increasing in demand. Thus, thin film transistor liquid crystaldisplay (TFT-LCD) devices having good image reproduction and reducedthickness have been developed. In addition, LCD devices have graduallygrown large in display area.

In general, a liquid crystal display (LCD) device includes twosubstrates, which are spaced apart and facing each other, and a liquidcrystal layer interposed between the two substrates. Each of thesubstrates includes an electrode, and the electrodes of each substrateare also facing each other. Voltage is applied to each electrode, andthus an electric field is induced between the electrodes. Alignment ofthe liquid crystal molecules is changed by the varying intensity ordirection of the electric field. The LCD device displays a picture byvarying transmissivity of the light varying according to the arrangementof the liquid crystal molecules.

A conventional LCD device will be described hereinafter in detail withreference to figures.

FIG. 1 is an exploded perspective view illustrating a conventional LCDdevice. As shown in FIG. 1, the conventional LCD device 11 has upper andlower substrates 5 and 22, which are spaced apart from and facing eachother, and also has liquid crystal 14 interposed between the uppersubstrate 5 and the lower substrate 22.

The upper substrate 5 includes a black matrix 6, a color filter layer 7,and a common electrode 18 subsequently on the inside (i.e., the sidefacing the lower substrate 22). The black matrix 6 has an opening. Thecolor filter layer 7 corresponds to openings in the black matrix 6 andincludes three sub-color filters of red (R), green (G), and blue (B).The common electrode 18 is formed on the color filter 7 and istransparent.

At least one gate line 13 and at least one data line 15 are formed onthe inner surface of the lower substrate 22 (i.e., the side facing theupper substrate 5). The gate line 13 and the date line 15 cross eachother to define a pixel area P. A thin film transistor T, as a switchingelement, is formed at the crossing of the gate line 13 and the data line15. The thin film transistor T includes a gate electrode, a sourceelectrode and a drain electrode. A plurality of such thin filmtransistors is arranged in a matrix form to correspond to othercrossings of gate and data lines 13 and 15. A pixel electrode 17, whichis connected to the thin film transistor T, is formed in the pixel areaP. The pixel electrode 17 corresponds to the sub-pixel color filter, andis made of a transparent conductive material such as indium-tin-oxide(ITO) that transmits light. The lower substrate 22, which includes thethin film transistors T and the pixel electrodes 17 arranged in thematrix form may be commonly referred to as an array substrate.

Although not shown in the figure, the LCD device further includes abacklight as a light source and a printed circuit board (PCB) includingdriver integrated circuits (ICs) as a driving element. The uppersubstrate 5 and the lower substrate 22 having the liquid crystal layer14 therebetween may be commonly referred to as a liquid crystal cell oras a liquid crystal panel.

A liquid crystal (LC) cell having twisted nematic (TN) mode is widelyused. Liquid crystal molecules in the TN mode LC cell have rod shapesthat are thin and long and that are helically twisted such that longaxes of the liquid crystal molecules are progressively changed, having auniform pitch.

In the TN mode, incident polarized light has different characteristicsof viewing angles according to arrangements of long axes and short axesof the liquid crystal molecules. That is, viewing angles of the LCDdevice are made along the long axes of the liquid crystal moleculeshaving a helical structure, and thus the viewing angles are varieddepending on a viewing direction.

Generally, the liquid crystal display device has a symmetric horizontalviewing angle range of about +45 degrees to about −45 degrees and avertical viewing angle range of about −15 degrees to about +15 degrees.Accordingly, images may be easily distorted in the vertical direction asthe viewing angles get narrow.

In the case of small size LCD devices, the display is seen from limitedangles by a few users. As LCD displays grow larger, the LCD device maybe watched from a wider variety of angles by a lot of users at the sametime. In these situations, the narrow viewing angles of the LCD devicemay cause problems.

To overcome the limited viewing angles of the LCD device, various modes,such as a film-compensated mode, a multi-domain mode, an in-planeswitching (IPS) mode, and so forth, have been proposed. In thefilm-compensated mode, a compensating film or a diffusing film may beused. In the multi-domain mode, a pixel is divided into several domainsand one domain has an arrangement direction different from otherdomains, thereby compensating the viewing angle. In the IPS mode, twoelectrodes for driving LC molecules are disposed on one substrate,whereby an electric field is induced in plane.

However, the LCD device has only a wide viewing angle mode, and theviewing angle mode cannot be changed according to circumstances, forexample, a display for a cash dispenser of a bank that requiressecurity.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay device having variable viewing angles that substantiallyobviates one or more of problems due to limitations and disadvantages ofthe related art.

An advantage of the present invention is to provide a liquid crystaldisplay device having variable viewing angles that is used as a wideviewing angle mode or as a narrow viewing angle according tocircumstances.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a liquidcrystal display device having variable viewing angles includes a firstliquid crystal cell having first and second substrates spaced apart fromand facing each other, a pixel electrode formed on an inner surface ofthe first substrate, a common electrode formed on an inner surface ofthe second substrate, and a first liquid crystal layer interposedbetween the pixel electrode and the common electrode; a second liquidcrystal cell on the first liquid crystal cell, the second liquid crystalcell having third and fourth substrates spaced apart from and facingeach other, a first alignment layer formed on an inner surface of thethird substrate, a second alignment layer formed on an inner surface ofthe fourth substrate, and a second liquid crystal layer interposedbetween the first and second alignment layers, wherein the first andsecond alignment layers are arranged to have holographic patterns; and aswitching part for selectively applying electric field to the secondliquid crystal layer.

In another aspect of the present invention, a liquid crystal displaydevice having variable viewing angles includes a first substrate; apixel electrode on a first surface of the first substrate; a firstliquid crystal layer on the pixel electrode; a common electrode on thefirst liquid crystal layer; a second substrate on the common electrode;a third substrate on the second substrate; a first alignment layer onthe third substrate and arranged to have holographic patterns; a secondliquid crystal layer on the first alignment layer; a second alignmentlayer on a the second liquid crystal layer and arranged to haveholographic patterns; a fourth substrate on the second alignment layer;a switching part selectively apply electric field to the second liquidcrystal layer.

In another aspect of the present invention, a liquid crystal displaydevice having variable viewing angles includes a first liquid crystalcell having first and second substrates spaced apart from and facingeach other, a pixel electrode formed on an inner surface of the firstsubstrate, a common electrode formed on an inner surface of the secondsubstrate, and a first liquid crystal layer interposed between the pixelelectrode and the common electrode; a second liquid crystal cell on thefirst liquid crystal cell, the second liquid crystal cell having thirdand fourth substrates spaced apart from and facing each other and asecond liquid crystal layer interposed between the third and fourthsubstrates, wherein the second liquid crystal layer includes discoticliquid crystal; and a switching part for selectively applying electricfield to the second liquid crystal layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is an exploded perspective view illustrating a conventionalliquid crystal display (LCD) LCD;

FIG. 2 is a schematic cross-sectional view of a liquid crystal display(LCD) device according to a first embodiment of the present invention;

FIG. 3A is a plan view schematically illustrating the second liquidcrystal cell of the LCD device of the first embodiment when an electricfield is not applied, and FIG. 3B is a plan view schematicallyillustrating the second liquid crystal cell of the LCD device of thefirst embodiment when an electric field is applied;

FIGS. 4A and 4B are cross-sectional views along the line IVA-IVA of FIG.3A and the line IVB-IVB of FIG. 3B, respectively;

FIG. 5 is a schematic cross-sectional view of an LCD device according toa second embodiment of the present invention;

FIG. 6A is a cross-sectional view schematically illustrating the LCDdevice of the second embodiment when an electric field is not applied,and FIG. 6B is a cross-sectional view schematically illustrating the LCDdevice of the second embodiment when an electric field is applied; and

FIG. 7 is a schematic cross-sectional view illustrating an LCD deviceaccording to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 is a schematic cross-sectional view of a liquid crystal display(LCD) device according to a first embodiment of the present invention.

As illustrated in FIG. 2, a first substrate 110 and a second substrate120 are spaced apart from and facing each other. A pixel electrode 112and a common electrode 122 are formed on inner surfaces of the first andsecond substrates 110 and 120, respectively. A first liquid crystallayer 130 is interposed between the pixel electrode 112 and the commonelectrode 122. The first substrate 110, the second substrate 120 and thefirst liquid crystal layer 130 constitute a first liquid crystal cellLC1.

Although not shown in the figure, a thin film transistor (TFT) may beformed on the inner surface of the first substrate 110 and may beconnected to the pixel electrode 112. A color filter layer may be formedbetween the second substrate 120 and the common electrode 122.

A first polarizer 140 is disposed on an outer surface of the firstsubstrate 110 and a backlight (not shown) is located on an outer surfaceof the first polarizer 140 to provide light.

A second liquid crystal cell LC2 is disposed on an outer surface of thesecond substrate 120 and a second polarizer 180 is situated on thesecond liquid crystal cell LC2. The second liquid crystal cell LC2includes a third substrate 150, a fourth substrate 160 and a secondliquid crystal layer 170 interposed therebetween.

Although not shown in the figure, first and second electrodes are formedon inner surfaces of the third and fourth substrates 150 and 160,respectively. The first and second electrodes are connected to an outervoltage source Vg1 through a switch S1, wherein the voltage source Vg1and the switch S1 constitute a switching part. The voltage source Vg1and the switch S1 are only one example for selectively applying anelectric field to the second liquid crystal layer 170, and other methodsmay be used.

In addition, alignment layers are formed on the first and secondelectrodes, respectively. The alignment layers are arranged usingholographic patterns, and LC molecules of the second liquid crystallayer 170 may form interference patterns by the arranged alignmentlayers. Therefore, light is diffused due to the interference patterns.

However, when an electric field is induced in the second liquid crystallayer 170, LC molecules of the second liquid crystal layer 170 all arearranged vertically or horizontally with respect to the electric field.Thus, diffusion effects of light are not shown.

The third and fourth substrates 150 and 160 may be made of glass,plastics or resin. The third and fourth substrates 150 and 160,beneficially, may be made in a form of an adhesive film by forming anelectrode and an alignment layer on one side of a flexible film andcoating an adhesive material on the other side of the flexible film.

In FIG. 2, the pixel electrode of each pixel and the common electrode inthe first liquid crystal cell LC1 are driven according to gate and datasignals, whereby the first liquid crystal cell LC1 provides light ofnarrow viewing angles to the second liquid crystal cell LC2. The secondliquid crystal cell LC2 supplied the light of the narrow viewing anglesfrom the first liquid crystal cell LC1 may be used in two modes.

In case of requiring wide viewing angles, that is, when a plurality ofusers watches a liquid crystal display (LCD) device from various angles,for example, the LCD device is driven turning off the switch S1. If theswitch S1 is turned off, voltage from the voltage source Vg1 is notsupplied to the second liquid crystal cell LC2. Therefore, the liquidcrystal molecules of the second liquid crystal layer 170 are arrangedalong the surfaces of the alignment layers that are arranged to haveholographic patterns, thereby diffusing light.

Meanwhile, in case of requiring narrow viewing angles, that is, when afew users sees the LCD device from limited angles, for example, the LCDdevice is driven by turning on the switch S1. If the switch S1 is turnedon, voltage from the voltage source Vg1 is supplied to the second liquidcrystal cell LC2. Accordingly, the liquid crystal molecules of thesecond liquid crystal layer 170 are arranged perpendicularly or parallelwith respect to an induced electric field regardless of the arrangementdirection of the alignment layer, thereby transmitting light only incertain directions.

Therefore, the viewing angles of the LCD device can be varied asoccasion demands.

The second liquid crystal cell LC2 will be explained in detail withreference to attached drawings.

FIG. 3A is a plan view illustrating the second liquid crystal cell ofthe liquid crystal display (LCD) device according to the firstembodiment of the present invention when an electric field is notapplied, and FIG. 3B is a plan view illustrating the second liquidcrystal cell of the LCD device according to the first embodiment of thepresent invention when an electric field is applied. FIGS. 4A and 4B arecross-sectional views along the line IVA-IVA of FIG. 3A and the lineIVB-IVB of FIG. 3B, respectively.

As shown in the figures, the second liquid crystal cell LC2 includes thethird and fourth substrates 150 and 160 spaced apart from and facingeach other. First and second electrodes 151 and 161 are formed on innersurfaces of the third and fourth substrates 150 and 160, respectively,and first and second alignment layers 152 and 162 are formed on thefirst and second electrodes 151 and 161, respectively. The second liquidcrystal layer 170 is interposed between the first and second alignmentlayers 152 and 162.

The first and second electrodes 151 and 161 are connected to the outervoltage source Vg1 of FIG. 2 through the switch S1 to induce an electricfield in the second liquid crystal layer 170.

The first and second alignment layers 150 and 160 are arranged to havecharacteristics of holographic patterns. That is, the second liquidcrystal cell LC2 has a first region A and a second region B, which aredifferently oriented. Each region of the alignment layers 150 and 160may have one of vertical, horizontal and hybrid modes.

As shown in FIGS. 3A and 4A, when an electric field is not applied,liquid crystal molecules of the second liquid crystal layer 170 arearranged along an alignment direction of alignment layers 152 and 162.Therefore, the liquid crystal molecules of the second liquid crystallayer 170 in the first region A and the second region B are arranged ina different direction from each other. Thus, light passing through thesecond liquid crystal cell LC2 is shown in holographic patterns. At thistime, a modulation depth d′, which is a thickness of the second liquidcrystal layer 170 that the light experiences based on the holographicpatterns, differs from the real thickness of the second liquid crystallayer 170, whereby retardation d′Δn of the light also differs from realretardation dΔn and the light is diffused. Accordingly, wide viewingangles can be achieved.

As shown in FIGS. 3B and 4B, when the electric field is applied, theliquid crystal molecules are arranged horizontally or vertically withrespect to the electric field according to properties of the liquidcrystal molecules. Thus, the liquid crystal molecules in the first andsecond regions A and B are arranged in the same direction. The secondliquid crystal cell LC2 does not diffuse the light and maintains narrowviewing angles provided from the first liquid crystal cell LC1 of FIG.2.

FIG. 5 is a schematic cross-sectional view of a liquid crystal display(LCD) device according to a second embodiment of the present invention.

As illustrated in FIG. 5, a first substrate 210 and a second substrate220 are spaced apart from and facing each other. A pixel electrode 212and a common electrode 222 are formed on inner surfaces of the first andsecond substrates 210 and 220, respectively. A first liquid crystallayer 230 is interposed between the pixel electrode 212 and the commonelectrode 222. The first substrate 210, the second substrate 220 and thefirst liquid crystal layer 230 constitute a first liquid crystal cellLC1. The first liquid crystal layer 230 has a twisted nematic (TN) mode.

Although not shown in the figure, a thin film transistor (TFT) may beformed on the inner surface of the first substrate 210 and may beconnected to the pixel electrode 212. A color filter layer may be formedbetween the second substrate 220 and the common electrode 222.

A second liquid crystal cell LC2 is formed on an outer surface of thesecond substrate 220. The second liquid crystal cell LC2 includes thirdand fourth substrates 240 and 260 that are spaced apart from and facingeach other and a second liquid crystal layer 250 that is interposedtherebetween. A first electrode 242 is formed on an inner surface of thethird substrate 240, that is, between the third substrate 240 and thesecond liquid crystal layer 250. A second electrode 262 is formed on aninner surface of the fourth substrate 260, that is, between the fourthsubstrate 260 and the second liquid crystal layer 250. The first andsecond electrodes 242 and 262 are connected to an outer switching partSW, which includes a voltage source Vg2 and a switch S2. The voltagesource Vg2 and the switch S2 are only one example for selectivelyapplying an electric field to the second liquid crystal layer 250, andother methods may be used.

The second liquid crystal layer 250 includes discotic liquid crystalmolecules of disk shapes. The discotic liquid crystal molecules havecharacteristics of wide viewing angles by diffusing light when anelectric field is not applied. When an electric field is applied, thediscotic liquid crystal molecules have characteristics of narrow viewingangles by being arranged horizontally or vertically with respect to theelectric field.

A third liquid crystal cell LC3 is formed on an outer surface of thefirst substrate 210. The third liquid crystal cell LC3 includes fifthand sixth substrates 270 and 290 that are spaced apart from and facingeach other and a third liquid crystal layer 280 interposed therebetween.A third electrode 272 is formed on an inner surface of the fifthsubstrate 270, that is, between the fifth substrate 270 and the thirdliquid crystal layer 280. A fourth electrode 292 is formed on an innersurface of the sixth substrate 290, that is, between the sixth substrate290 and the third liquid crystal layer 280. The third liquid crystallayer 280 also includes discotic liquid crystal molecules.

Meanwhile, the third and fourth electrodes 272 and 292 may be alsoconnected to the switching part SW. In this case, voltage may be appliedor may be not applied to the second and third liquid crystal layers 250and 280 at the same time.

A first polarizer 294 and a second polarizer 264 are situated on outersurfaces of the third liquid crystal cell LC3 and the second liquidcrystal cell LC2, respectively, and although not shown in the figure, abacklight is located on an outer surface of the first polarizer 294 toprovide light.

The third, fourth, fifth and sixth substrates 240, 260, 270 and 290 maybe made of one of glass, plastics and resin and beneficially, may bemade in a form of an adhesive film by forming an electrode and analignment layer on one side of a flexible film and coating an adhesivematerial on the other side of the flexible film.

The second and third liquid crystal layers 250 and 280 may have one ofhorizontal, vertical, hybrid, incline, and twist modes depending onoptical characteristics of the first liquid crystal layer 230 and may bearranged differently at each pixel if viewing angles and brightnessshould be controlled.

In FIG. 5, the third liquid crystal cell LC3 may be used to be connectedto the switching part SW, but can be used separately not to be connectedto the switching part SW. If the third liquid crystal cell LC3 is notconnected to the switching part SW, the third liquid crystal cell LC3acts as an element for increasing efficiency in condensing light or acompensating plate. If the third liquid crystal cell LC3 is connected tothe switching part SW, the third liquid crystal cell LC3 changes viewingangles the same as the second liquid crystal cell LC2.

The pixel electrode of each pixel and the common electrode in the firstliquid crystal cell LC1 are driven according to gate and data signals,whereby the first liquid crystal cell LC1 provides light passing throughthe third liquid crystal cell LC3 to the second liquid crystal cell LC2such that the light passing through the third liquid crystal cell LC3should be changed to have narrow viewing angles.

The second liquid crystal cell LC2 supplied the light of the narrowviewing angles from the first liquid crystal cell LC1 may be used in twomodes.

In case of requiring wide viewing angles, that is, when a plurality ofusers watches a liquid crystal display (LCD) device from various angles,for example, the LCD device is driven turning off the switch S2. If theswitch S2 is turned off, a voltage from the voltage source Vg2 is notsupplied to the second liquid crystal cell LC2. Therefore, the secondliquid crystal layer 250 including discotic liquid crystal moleculesdiffuses light.

Meanwhile, in case of requiring narrow viewing angles, that is, when fewusers see the LCD device from limited angles, for example, the LCDdevice is driven turning on the switch S2. If the switch S2 is turnedon, the voltage from the voltage source Vg2 is supplied to the secondliquid crystal cell LC2. Accordingly, the liquid crystal molecules ofthe second liquid crystal layer 250 are arranged perpendicularly orparallel with respect to an induced electric field, thereby transmittinglight only in certain directions.

Therefore, the viewing angles of the LCD device can be varied asoccasion demands.

Movements in the second and third liquid crystal layers will beexplained in detail with reference to attached drawings.

FIG. 6A is a cross-sectional view schematically illustrating the liquidcrystal display device according to the second embodiment of the presentinvention when an electric field is not applied, and FIG. 6B is across-sectional view schematically illustrating the liquid crystaldisplay device according to the second embodiment of the presentinvention when an electric field is applied.

As shown in FIG. 6A, in the first liquid crystal cell LC1 including thefirst substrate 210, the second substrate 220 and the first liquidcrystal layer 230, the first liquid crystal layer 230 is driven by gateand data signals. At this time, an electric field is not induced in thesecond liquid crystal cell LC2, which includes the third substrate 240,the fourth substrate 260 and the second liquid crystal layer 250, and inthe third liquid crystal cell LC3, which includes the fifth substrate270, sixth substrate 290 and the third liquid crystal layer 280, wherebythe second and third liquid crystal layers 250 and 280, which are madeof discotic liquid crystal molecules, diffuse light.

As shown in FIG. 6B, when electric field is induced in the second andthird liquid crystal cell LC2 and LC3, the discotic liquid crystalmolecules are arranged vertically or horizontally with respect to theinduced electric field. In this case, the second and third liquidcrystal layers 250 and 280 transmit light in a certain direction thesame as normal liquid crystal, and thus the liquid crystal displaydevice has narrow viewing angles.

As stated above, in the second embodiment of the present invention, thefirst liquid crystal layer 230 may use TN liquid crystal and the secondand third liquid crystal layers 250 and 280 may include discotic liquidcrystal molecules. In addition, the second and third liquid crystallayers 250 and 280 may have one of vertical, horizontal and hybridmodes.

Meanwhile, the third liquid crystal cell LC3 may be connected to theswitching part SW of FIG. 5, but the third liquid crystal cell LC3 mayfunction simply as a compensating plate without connection with theswitching part SW. Although the third liquid crystal cell LC3 isconnected to the switching part SW, the third liquid crystal cell LC3can be driven independently on the second liquid crystal cell LC2.

On the other hand, liquid crystal of vertical alignment mode may be usedas material for the first liquid crystal layer.

FIG. 7 is a schematic cross-sectional view of illustrating a liquidcrystal display device according to a third embodiment of the presentinvention. As shown in FIG. 7, the liquid crystal display device of thethird embodiment includes a first liquid crystal cell LC1 and a secondliquid crystal cell LC2 on the first liquid crystal cell LC1. The firstliquid crystal cell LC1 has a first substrate 310, a second substrate320, and a first liquid crystal layer 330 therebetween. A pixelelectrode 312 and a common electrode 322 are formed on inner surfaces ofthe first and second substrates 310 and 320, respectively. The firstliquid crystal layer 330 has a vertical alignment mode, where liquidcrystal molecules are initially arranged vertically with respect to thesubstrates.

A first polarizer 370 is disposed on an outer surface of the firstsubstrate 310. Although not shown in the figure, a backlight is locatedon the first polarizer 370, that is, on an outer surface of the firstpolarizer 370, as a light source.

The second liquid crystal cell LC2 is formed on an outer surface of thesecond substrate 320. The second liquid crystal cell LC2 includes thirdand fourth substrates 340 and 360 that are spaced apart from and facingeach other and a second liquid crystal layer 350 that is interposedbetween the third and fourth substrates 340 and 360. A first electrode342 and a second electrode 362 are formed on inner surfaces of the thirdand fourth substrates 340 and 360, respectively. The second liquidcrystal layer 350 may include discotic liquid crystal molecules.

The first and second electrodes 342 and 362 are connected to an outerswitching part SW, which includes a switch S3 and a voltage source Vg3.The voltage source Vg3 and the switch S3 are only one example forselectively applying an electric field to the second liquid crystallayer 350, and other methods may be used.

A second polarizer 380 is situated on an outer surface of the fourthsubstrate 360.

The third and fourth substrates 340 and 360 may be made of one of glass,plastics and resin and beneficially, may be made in a form of anadhesive film by forming an electrode and an alignment layer on one sideof a flexible film and coating an adhesive material on the other side ofthe flexible film.

The second liquid crystal layer 350 may have one of horizontal,vertical, hybrid, incline, and twist modes depending on opticalcharacteristics of the first liquid crystal layer 330 and may bearranged differently at each pixel if viewing angles and brightnessshould be controlled.

In FIG. 7, the pixel electrode of each pixel and the common electrode inthe first liquid crystal cell LC1 are driven according to gate and datasignals, whereby the first liquid crystal cell LC1 provides light ofnarrow viewing angles to the second liquid crystal cell LC2. The secondliquid crystal cell LC2 supplied the light of the narrow viewing anglesfrom the first liquid crystal cell LC1 may be used in two modes.

In case of requiring wide viewing angles, that is, when a plurality ofusers watches a liquid crystal display (LCD) device from various angles,for example, the LCD device is driven turning off the switch S3. If theswitch S3 is turned off, a voltage from the voltage source Vg3 is notsupplied to the second liquid crystal cell LC2. Therefore, the secondliquid crystal layer 350 including discotic liquid crystal moleculesdiffuses light.

Meanwhile, in case of requiring narrow viewing angles, that is, when afew users sees the LCD device from limited angles, for example, the LCDdevice is driven turning on the switch S3. If the switch S3 is turnedon, the voltage from the voltage source Vg3 is supplied to the secondliquid crystal cell LC2. Accordingly, the liquid crystal molecules ofthe second liquid crystal layer 350 are arranged perpendicularly orparallel with respect to an induced electric field, thereby transmittinglight only in certain directions.

Therefore, the viewing angles of the LCD device can be varied asoccasion demands.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the fabrication andapplication of the present invention without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

1. A liquid crystal display device having variable viewing angles,comprising: a first liquid crystal cell having first and secondsubstrates spaced apart from and facing each other, a pixel electrode onan inner surface of the first substrate, a common electrode on an innersurface of the second substrate, and a first liquid crystal layerinterposed between the pixel electrode and the common electrode; asecond liquid crystal cell on the first liquid crystal cell, the secondliquid crystal cell having third and fourth substrates spaced apart fromand facing each other and a second liquid crystal layer interposedbetween the third and fourth substrates, wherein the second liquidcrystal layer includes discotic liquid crystal having an initialalignment of molecules of the second liquid crystal layer to diffuselight transmitted through the first liquid crystal cell over a firstviewing angle; and a switching part that selectively applies an electricfield to the second liquid crystal layer that aligns the molecules ofthe second liquid crystal layer to diffuse light transmitted from thefirst liquid crystal cell over a second viewing angle smaller than thefirst viewing angle.
 2. The device according to claim 1, wherein thefirst liquid crystal layer has a vertical alignment mode, wherein liquidcrystal molecules of the first liquid crystal layer are initiallyarranged with respect to the first and second substrates.
 3. The deviceaccording to claim 2, wherein the second liquid crystal cell furtherincludes a first electrode between the third substrate and the secondliquid crystal layer and a second electrode between the fourth substrateand the second liquid crystal layer.
 4. The device according to claim 3,wherein the switching part is connected to the first and secondelectrodes.
 5. The device according to claim 1, further comprising afirst polarizer on an outer surface of the first substrate and a secondpolarizer on an outer surface of the fourth substrate.
 6. The deviceaccording to claim 1, further comprising a third liquid crystal cell onan outer surface of the first substrate, wherein the third liquidcrystal cell includes fifth and sixth substrates spaced apart from andfacing each other and a third liquid crystal layer interposed betweenthe fifth and sixth substrates, wherein the third liquid crystal layerincludes discotic liquid crystal.
 7. The device according to claim 6,wherein the second liquid crystal cell further includes a firstelectrode between the third substrate and the second liquid crystallayer and a second electrode between the fourth substrate and the secondliquid crystal layer.
 8. The device according to claim 7, wherein theswitching part is connected to the first and second electrodes.
 9. Thedevice according to claim 8, wherein the third liquid crystal cellfurther includes a third electrode between the fifth substrate and thethird liquid crystal layer and a fourth electrode between the sixthsubstrate and the third liquid crystal layer.
 10. The device accordingto claim 9, wherein the switching part is connected to the third andfourth electrodes.
 11. The device according to claim 10, wherein theswitching part includes a voltage source and a switch.
 12. The deviceaccording to claim 6, wherein the third, fourth, fifth and sixthsubstrates includes one of glass, plastics and resin.
 13. The deviceaccording to claim 12, wherein the third, fourth, fifth and sixthsubstrates are made of a flexible adhesive film.
 14. The deviceaccording to claim 6, wherein the second and third liquid crystal layershave one of vertical, horizontal and hybrid modes.
 15. The deviceaccording to claim 6, further comprising a first polarizer on an outersurface of the sixth substrate and a second polarizer on an outersurface of the fourth substrate.
 16. The device according to claim 15,further comprising a backlight on an outer surface of the firstpolarizer.
 17. The device according to claim 6, wherein the first liquidcrystal layer is a twisted nematic mode liquid crystal layer.